Re: [PATCH v2 18/19] drivers: mem: Create file to access second half of 64-bit memory

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On Thu, Jan 31, 2019 at 01:54:52PM +0300, Peter Mamonov wrote:
> Hello, Andrey,
> 
> > In order to allow access to second half of address space on 64-bit
> > machines, add code that creates /dev/highmem dedicated for that.
> > 
> > Note that due to maximum file size being limited to MAX_LFS_FILESIZE
> > or 0x7fff_ffff_ffff_ffff bytes at addresses 0x7fff_ffff_ffff_ffff and
> > 0xffff_ffff_ffff_ffff cannot be access through /dev/mem and
> > /dev/hightmem correspondingly.
> 
> Does it imply using `-s /dev/highmem` argument when accessing addresses beyond 
> MAX_LFS_FILESIZE? That's not very convenient:
> 
> 	$ git grep -l /dev/mem
> 	commands/crc.c
> 	commands/digest.c
> 	commands/disasm.c
> 	commands/md.c
> 	commands/memcmp.c
> 	commands/memcpy.c
> 	commands/memset.c
> 	commands/mm.c
> 	commands/mw.c

I've forgotten to mention, that all meaningful MIPS64 virtual addresses  
belong to the 2nd half of the address space. Except for user segment addresses 
which are not used in barebox.

> 
> Regards,
> Peter

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